High sensitivity magnetic relay



Oct. 27, 1964 E. w. BORDENET 3,

HIGH SENSITIVITY MAGNETIC RELAY Filed Dec. 22, 1961 4 Sheets-Sheet 1 S/G'NA CUEEE/VT SOURCE INVENTOR. Eueem: W. BORDENET Oct. 27, 1964 w. BORDENET HIGH SENSITIVITY MAGNETIC RELAY Filed Dec. 22, 1961 4 Sheets-Sheet 2 RT. S. E Y MN T N M E V N E 0a. 27, 1964 E. w. B-ORDENET HIGH SENSITIVITY MAGNETIC RELAY Filed Dec. 22-, 1961 4 Sheets-Sheet 3 s s ii) RSI R35 hm? x Y S 9] I NVEN TOR. EUGENE W. Bonosue'r Oct. 27, 1964 E. w. BORDENET 3,154,728

HIGH SENSITIVITY MAGNETIC RELAY Filed Dec. 22-, 1961 4 Sheets-Sheet 4 NULL TORQUE "Y" SWITCH INVENTOR. OPERATION EUGENE w. BOROENET Lid/9W 4 Arrvs.

E AU w W 2. M w .w% 1 M e u E (P H 8 2m 5 M n T E 1 N M R l\ W r uw 0R U m TT M 1 IA I I I I Ill m M H W T M 7 M I mm 1| I -iilrl MT ll m w 1 w M m T Wm m Aw Wm PM L (J m0 N F ME 6 i (T Cm I A r T TL WT N 0R .L e I I l .l- E k n P Q \XO .L /7 T 0 maemE- United States Patent 3,154,728 HIGH SENSITIVITY MAGNETIC RELAY Eugene W. Bordenet, Rockford, Ill., assignor to Barber- Colman Company, Rockford, 111., a corporation of Illinois Filed Dec. 22, 1961, Ser. No. 161,522 4 Claims. (Cl. 317-450) This invention relates to improved magnetic circuit relays and more particularly to an improvement in magnetic relays of a type disclosed in Bullen and Anderson, United States Patent No. 2,443,784, issued June 22, 1948. Such magnetic relays have been advantageously employed in switch installations where stability, compactness, and rugged construction are required in addition to high sensitivity. These relays, in eifect, perform as amplifiers with a relatively small excitation unbalancing a large amplitude, steady state flux field controlling the movement of an armature. This type of relay is also particularly adapted for use as a polarized relay in which the direction of the input excitation current determines the direction of movement of the armature.

It is the principal object of the invention to further increase the sensitivity of such magnetic relays.

It is also an object of the invention to provide a magnetic relay affording high sensitivity without critical adjustment or loss of stability.

Moreover, it is an object to provide increased relay sensitivity by a very simple change without in any Way subtracting from such advantageous characteristics as compactness, ruggedness or economy of manufacture.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIGURE 1 is an end elevation of a polarized relay embodying the present invention;

FIG. 2 is an enlarged transverse sectional view taken along lines 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary perspective view of the paramagnetic elements of the relay, the other parts being removed;

FIG. 4 is an exploded view of the armature and input coil assembly of the relay of FIG. 1;

FIG. 5 is a section in perspective along lines 5-5 of FIG. 3 With cross hatching removed from the sectioned faces to facilitate illustration of flux paths.

FIG. 6 is a scaled drawing of a portion of the paramagnetic elements shown in FIG. 2 to illustrate the relative air gap sizes in a particular example of a relay represented in FIG. 1;

FIG. 7 is an end view of the paramagnetic elements shown in FIGS. 6 and 7 drawn to the same scale;

FIG. 8 is a simplified schematic diagram illustrating the principal reluctances of the relay magnetic circuit when the armature is in a magnetic neutral position;

FIG. 9 is a simplified schematic diagram further illustrating the relay reluctances elfective in the magnetic circuit when the armature is displaced from a magnetic neutral position;

FIG. 10 is another schematic circuit of the reluctances of the relay indicating still further reluctances elements likely to be elfective under certain relay operating conditions;

FIG. 11 is a schematic representation (not to scale) of the magnetic elements shown in FIG. 6 and illustrating effective flux paths when the armature is deflected in a counterclockwise direction;

FIG. 12 is a schematic representation (not to scale) of the magnetic elements shown in FIG. 6 and illustrating effective flux paths when the armature is deflected in a clockwise direction;

FIG. 13 is a generalized plot of relay input torque, magnetic torque and restoring torque with respect to angular deflection in either direction from a magnetic neutral position; and

FIG. 14 is a more detailed analysis of input, magnetic and restoring torques with respect to angular deflection and further showing the net effective torque for a particular adjustment and input excitation.

While the invention will be described in connection with preferred embodiments, it will be understood that I do not intend to limit the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents, falling within the spirit and scope of the invention and defined by the appended claims.

Referring first to FIGS. 1 and 2, a relay 29 is shown therein of the type described at length in the aforementioned Bullen et al. Patent No. 2,443,784. In such a relay an armature assembly 21 is angularly deflected or tilted about a central axis in either direction from a central horizontal position to provide the desired switching action. In this instance, stationary switch contacts 22 and 23 are positioned under opposite ends of the armature assembly. Deflection of the armature in a counterclockwise direction (as oriented in FIG. 2) closes the circuit between the armature and stationary contact 22 while deflection in the clockwise direction closes the circuit between the armature and contact 23. The stationary contacts also serve to limit the armature movement which, while small, acts with suflicient force and speed for relatively large power ratings. Normally, closed contact pairs or various combinations of switches may be employed as desired for particular purposes.

The direction of the armature movement is controlled by the direction of the magnetizing input currents in a stationary coil assembly 24 which surrounds the armature. A magnetic stator assembly 25 defines air gaps within which end portions of the armature assembly move, the magnetic flux distributed by the gaps being supplied by permanent magnets 26 and 27. The entire assembly is shown mounted on a base 28 provided with electrical plug-in connectors 29 for the coil assembly and switching contacts. A cover 30 encloses the unit. As indicated in block form in FIG. 1, a signal current source is suitably connected to the terminals of the coil 24 through the plug in connector 29 as indicated in FIG. 1.

Referring more particularly to the armature assembly 21 as shown in FIG. 4, the armature 32 itself is a vane which is part of the magnetic circuit of the relay. It is preferably made of high permeability magnetic material such as a 50% nickel-50% iron alloy. For most applications it is also desirable that the armature have very little retentivity. Towards that end the central portion 33 of the armature 32 is reduced in cross section area to limit by saturation the amount of flux carried by the armature and thus limit the retention level.

To facilitate mounting of the basic armature member 32 and to carry switch electrodes, a thin elongated carrier member 34, suitably made of beryllium copper or other resilient electrical conductor, is fastened to the armature. The ends of the carrier extend beyond the armature to engage the switching contacts 22 and 23. Torsion shafts or bars 35 extend laterally from the carrier to define a central axis of rotation for the armature. The torsion shafts are secured to mounting rails 36 suitably parallel to the carrier, sothat the entire armature assembly is flat and compact. The torsion shafts 35 function as resilient springs to provide a restoring torque for the armature which is proportional to deflection of the armature in either direction from a mechanical neutral position.

As further shown in FIG. 4, the armature assembly 21 is dimensioned to fit within the rectangular center opening of a bobbin 38 of the coil assembly 24. The

45, 45', 46,46. have flanges to serve as mounting brackets but the flanges play no appreciable role in the magnetic circuit. The

very critical operation.

bobbin itself is suitably made of insulating sheet mater-ial or molded of plastic. The coil 39 wound on the bobbin thus closely surrounds the armature assembly to induce a magnetomotive potential along the length- 'wise dimension of the armature 32 of a polarity deter-mined by the polarity of input excitation. The pole pieces position and support the mounting rails 36 and the small bobbin opening accommodates the degree of armature rotation required for switch actuators.

The magnetic structure in which the armature is employedand which is the focus of the remainder of the description is portrayed in FIG. 3, With the other portions of the relay such as the input coil and the switches removed. As shown therein, an upper plate 41 bridges the south poles of the permanent magnets 26 and 27,

while the lower plate 42 bridges the north poles of the magnets. The permanent magnets themselves are suitably a conventional highretentivity permanent magnet material, such as an Alnico magnetic alloy of aluminum, nickel and cobalt.

Closely spaced air gaps are defined between pole p ices defined by the facing edges of bent-down tabs 43 and 43 of the central portion of the bridging plate 41 and of bent-up tabs 44 and 44' of a central portion of the lower bridging plate 42. As shown in the FIG. 3 construction, the pole face area is increased by upper blocks 45 and 45' secured to the upper pole pieces 43 and 43 and by lower blocks 46 and 46 secured to lower pole pieces 44 and 44. In referring to the gaps and pole face areas in following portions of the specification, reference to the pole pieces is not intended to exclude the attached blocks The lower blocks conveniently also magnetic circuit members are all made high permeability 'material such as the nickel-iron material specified for "are provided which connect the upper pole pieces with intermediate portions of the permanent magnet blocks '26 and 27. As shows in FIGS. 1 and 3, straps 4S and wet ferromagnetic material are clamped to the upper pole piece surface 45. Their free ends are adjustab-ly positioned along the length of'the adjacent permanent magnetic blocks 26 and 27. A similar arrangement of shunt straps 45 and 49 is provided on the other upper pole piece surface 45. Lack of uniformity in the manufacture and assembly of the magnets of themselves or other elements of the magnetic circuit may cause nonuniform flux distribution in either gap or cause the flux -in the two gaps to differ from each other. By adjusting the straps a balance point can be reached. The reluctanceof the iron paths themselves, while small, cannot be assumed to be negligible, and balancing can be a A portion of the theoretically available flux is diverted when the shunt bars are moved downward to. reduce the flux density in the nearest gap,

but the small changes in the gap flux density are important in balancing the armature. This balancing operation is usually also combined with calibration so that operation of the relay will occur upon a given ampere-turns input to the winding or windings. As subsequently described,

' the amount of input excitation required can be decreased by raising the permanent magnetic flux in the gaps, but

adjustment difficulties and instability are likely to result. In accordance with the invention, stationary magnetic inserts t) and 51 have been provided. As indicated in FIGS. 2, 3, and 4. Insert 50 is positioned between the matica-lly illustrated in FIG. 8.

between each pair of split or like poles pieces. The plates themselves have a flat surface and are positioned parallel to and facing the general plane of the armature assembly. As further shown in FIGS. 2 and 4 the inserts may be conveniently fixed in place and spaced at each end from the pole pieces by positioning them on the upper and lowersides respectively of the empty coil bobbin 38 before it is wound. The inserts may also be embedded in the bobbin if a molded plastic bobbin is employed.

The exact theory of operation of the inserts and their role in the overall magnetic circuit of the relay has not been precisely determined. Nevertheless, they have been found to be very advantageously employed for increasing the relay sensitivity. That is, for a given armature stability at Zero excitation, the input excitation required to deflect the armature (and operate the switch) is appreciably decreased when the inserts are present. Conversely, for a given operating input excitation the magnet flux can be decreased and the armature stability at zero excitation increased.

The remaining figures, FIGS. 5-14, are directed to an explanation of the theory and operation significant in the structure thus far described. First, referring to FIG. 5,

flux paths q /2 and /2 are shown extending directly across the north and south pole gaps through the X and Y (left and right) ends of the armature 32 extending into the gaps. These paths represent an equal division of the total magnet torque through the gaps, occurring when the armature is in a neutral position and in the absence of the input excitatiaon flux The flux paths /2 and 2 are shown as complete circuits returning through one of the permanent magnets, but it will be appreciated that the magnet flux emanates from both magnets and is distributed through the entire magnetic structure. Slight reluctances of the ferromagnetic members and differences in the magnetomotive forces of the two magnets cause local variation of the flux density even when the armature is centered and input excitation is absent. For example, the flux path through the shunting strap 48 of shunting flux may affect both the local distribution of the useful flux a and reduce the magnetomotive force at the righthand gap.

Under the conditions of equal division of magnet flux, the fact that the mechanical center of the armature is also the magnetic neutral is easily demonstrated. For more clearly identifying the gap-s as well as providing a scale representation, to illustrate the relative reluctances, reference is made to the sealed gaps of the relay magnetic circuit portions shown in FIGS. 6 and 7. For convenience, the ends of the pole pieces 44 and 43 are indicated as N and S (for north and south polarities) while the ends of pole pieces 33 and Y33 are referred to as N and S. Thus the total gap between poles N and S is decreased by the armature and divided into two equal gaps g1 and g2. Likewise, the gap between poles N and S are divided into gaps g3 and g4. With the gaps equal to each other and using the symbol R for magnetic reluctance, the gap reluctances R R R and R are equal to each other. This simple circuit is sche- With equal magnetomotive forces from N to S and N to S, the X and Y ends of the armature are at the same magnetic potential. No flux is diverted through the armature even though it offers practically no reluctance.

An armature deflecting torque for changing the magnet flux balance is initiated by the input ampere turns. Referring again to FIG. 5, for one direction of input current an input flux 4: is induced in the armature which 'may divide into upper and lower /2 components in v.9 members defining a gap varies with the square of the fiux times the gap area, the counterclockwise torques on the armature in gaps g2 and g3 substantially exceeds the clockwise torques on the armature in gaps g1 and g4, thus causing an armature deflection in a counterclockwise direction. This torque component tends to remain constant as the armature deflection changes since the total gap reluctance R +R or R -t-R remain constant in either the upper or lower 2 circuit.

The torque component due to the input excitation is also believed to be increased by the further input flux 5 2 induced in each of the magnetic inserts 5t] and 51. Referring again to the gap scaled to dimensions set forth in FIGS. 6 and 7, the width of the bobbin sides interposed between the ends of the inserts and the pole pieces helps to define the fixed insert gaps. As shown in FIG. 6 these are g5 and g7 at the ends of insert 50 and g6 and g8 at the ends of insert 51. Approximating the area as the end of the insert (shown in FIG. 7) reluctances are readily computed as directly proportional to the gap length divided by the gap area. They permit substantial fluxes to be induced by the input signal in the magnetic inserts.

Referring back to FIG. 5 the upper input fiux /2 traces a circuit along insert 50, through g7, around the upper pole piece structure, and returning through g5 to the insert 50. A lower circuit is similarly traced through insert 51, g8, the lower pole piece assembly and returning through g6. While they do not pass through the main air gaps g1, g2, g3, and g4 they are believed to help cause a redistribution of the magnet flux assisting the torque in the direction initiated by the input flux The fluxes (p /2 may be noted to oppose the magnet flux in the upper left and lower right pole pieces in FIG. 5.

Once the armature has started to deflect, the magnet flux flow along its length is no longer zero. The initiating of a counterclockwise armature deflection in the FIG. 5 illustration results in the sum of gaps g2 and g3 becoming the shortest total gap from either lower pole piece to either upper pole piece. Under these conditions, with reluctances R or R each less than R or R the balance changes, and permanent magnet flux flows in the X to Y direction along the armature (the same direction as the flux initiating the deflection). The resultant flux through the armature is that illustrated in FIG. 11 as This flux is larger than either /2 (the initial magnet flux in either gap). As a result, the deflecting torque increases and continues to increase as the R and Bi decrease with further deflection. When the input current is in the opposite direction from that causing the input excitation flux in FIG. 3, the deflection begins in the clockwise direction. The magnet flux is unbalanced as shown in FIG. 12 to produce a dominant flux from pole N through g4, along the armature, and through g1 to pole S. This cross flux or diagonal transfer from one of the split like polarity pole-s along the armature to the remote one of the opposite polarity pair of split poles is characteristic of the deflecting armature component of the magnet flux torque.

In further accordance with the present invention the magnet flux torque is assisted by the further magnet flux paths through the stationary magnetic inserts 5t) and 51. The additional magnetic flux producing paths are shown as and in FIGS. 11 and 12. The portion of the additional sensitivity obtained in relays containing the magnetic inserts 5t) and 51 attributable to the torque caused by magnetic fluxes p and has not been positively ascertained. The existence of a helping torque is supported by computations, however. Referring again to the scaled gap representations in FIGS. 6 and 7, the overlying areas of insert 50 and the armature 33 define the areas of gaps g9 and gll. Gaps git) and g12 are similarly defined with respect to insert 51. The

6 gaps g9 and gll are but the halves of a total gap g9, 11 as divided by the armature axis. The gaps grit) and g12 may be similarly expressed as one gap gll), 12.

Referring again to FIG. 11, the path of magnet flux is traced from pole piece N through narrowed gap g2 along the insert 51 to the armature and thence through the narrowed gap g3 to pole piece S. Unless the armature is saturated at its mid region, the flux passage between the insert 51 and the armature is distributed throughout the air gaps glt) and g12 (see FIG. 6). The additional flux in gaps g3 results in additional force. Since force is proportional to the square of the total flux. Similarly the magnetic flux flowing through gap g2 and from the armature to the upper insert increases the counterclockwise torque on the X or left end of the armature.

If the flux (p or (p is distributed along the entire gap between the armature and insert, cancelling forces between them are set up on opposite sides of the armatune axis. Should the gap flux be distributed over only giZ or g9 in FiG. 11 (or to git and g1]; in FiG. 12), the force opposes the desired force direction but the opposing torque is much smaller for several reasons than that desirably added in the main gaps by (p or 5 The analysis of the added magnet torques due to the presence of the magnetic inserts and as expressed in terms of the added fiux paths qs and in FIGS. 11 and 12, appears entirely consistent with the results in fact achieved. It is recognized that further factors may play a role in explaining the effectiveness of the inserts. FIGS. 9 and 10, for example, are reluctance networks showing possible paths for magnet flux. Only the dominant paths of FIG. 9 have been described in the analysis of FIGS. 11 and 12. A more comprehensive network is portrayed in FIG. 10 in which R32 represents the reluctance of the armature mid portion when near saturation. Furthermore, since very small changes in reluctance are needed sufiicient to divert north to south pole flux from one of the split pole flux paths to the other, changes in the reluctances of portions of the iron circuit may themselves be of consequence. For this reason, FIG. 10 illustrates minor reluctances for the pole piece members 43, 43, 44 and 44-. Small reluctance changes are characteristic of the entire relay system, and the armature switching deflection itself is very small, being typically only a few hundredths of a degree.

The relay component torques are generally shown in FIG. 13 in which +0 and 0 as abscissae represent angular deflection of the armature and clockwise or counterclockwise torques are the ordinates all with respect to a center zero. The restoring torque of the spring is represented by the straight line Tr has a slope ,8 corresponding to the spring constant. Torque Tm due to the permanent magnet flux is also a straight line having an opposite slope oz. The input torque curve Ti is simply one of possible clockwise or counterclockwise values since it does not change with 0. When the sum of the input torque Ti and magnet torque Tm exceed the restoring torque Tr at any particular value of 0 the armature is moved toward its limit position. These are indicated as the X switch operation and the switch operation values of 6. If a is appreciably less than B, the armature is stable in a center neutral position until an input signal torque Ti is generated. If a is greater than 6 the armature is stable in whatever limit position to which it was deflected. If as equals 5 a very unstable condition results in which the armature is likely to bounce or flutter in the absence of an input signal torque.

For a particular example, reference is made to FIG. 14 in which, for a stable central position of the armature, the slope of the restoring torque Tr exceeds that of the magnet torque Tm. With a given input torque Ti, the armature is subject to a deflecting torque up to the null torque value of 0 for which the input Ti does not exceed the difference between the restoring torque Tr and the magnet torque Tm. In the example represented by FIG. 14, Ti is chosen of sufficient amplitude so that the value of for operating the Y contact is less than the null 0. The restoring torque curve may also be shifted along the abscissa in FIGS. 13 and 14 for desired relay operation with the zero torque at a chosen armature angle other than the mechanical center. In keeping suitable diiference between a and [i for stability, the magnetic slugs are believed to play a role as previously explained in both increasing the slope for the magnet torque Tm and in increasing the factor by which the input ampereturns is multipled in deriving the input torque Ti.

I claim as my invention:

1. A magnetic relay having in combination two laterally spaced sets of pole pieces, each set of pole pieces defining a gap between pole faces having opposite polarity, means for supplying equal magnetic fluxes in the same direction in each gap, a magnetic armature centrally pivoted between said laterally spaced sets of pole pieces for angular deflection with respect ends of the armature in the respective gaps, means for inducing an unbalancing flux along the armature in response to an input signal, and a magnetic insert positioned between the laterally spaced pole pieces on each side of the armature, each said insert being spaced from the pole pieces and the armature to define air gaps therewith.

2. A magnetic relay having in combination a magnetic circuit with a permanent magnet therein, a portion of said magnetic circuit being divided to form a pair of laterally spaced ferromagnetic stationary members, each having an air gap therein separating pole faces of opposite polarity, said air gaps being aligned along a common axis, a magnetic armature aligned with said axis and centrally pivoted between said members for angular deflection with respective ends of the armature in the respective air gaps, means for inducing an unbalancing flux in a selected direction along the armature in response to an input signal, and a magnetic insert positioned between the stationary members on each side of the armature, each said insert being spaced from the members and the armature to define air gaps therewith.

3. In a magnetic relay the combination comprising a source of magnetizing flux, a low permeability spaced parallel branch pole piece assembly in circuit therewith,

said pole pieces being interupted tovdefine small planar air gaps in each pole piece branch to form pole faces of opposite polarity, means for equalizing the flux from said source in said gaps, a magnetic planar armature centrally pivoted between the parallel branches for angular deflection with respective ends of the armature in the respective gaps, spring means for applying a centering torque to the armature, a stationary coil between said branches and surrounding a central portion of said armature, means for energizing said coil with an input signal to produce a magnetomotive force. along said armature in a direction corresponding to the signal polarity, and a planar magnetic insert positioned between the spaced branch pole pieces near the armature, said insert being spaced from the pole pieces and the armature to define air gaps therewith.

4. In a magnetic relay the combination comprising an elongated armature made of magnetic material and centrally pivoted for rotational displacement in either direction from a normal plane, spring means for restraining the armature movement from a normal balance position, stationary shunt members made of magnetic material respectively spaced above and below the plane of the armature, an energizing winding surrounding said shunt members and a central portion of said armature, a first pair of like-polarity pole pieces spaced above the normal plane of the armature near its ends, a second pair of likepolarity pole pieces but oppositein polarity from said first pair spaced below the normal plane of the armature near its ends, a permanent magnet in magnetic circuit between said first and second pairs of pole pieces to provide a steady state magnetic flux between pole pieces of opposing polarity, and means for supplying a signal current to said winding for producing an unbalancing flux in a selected direction along the armature and said shunt members corresponding to the polarity of said signal, said shunt members each having end portions respectively adjacent the pole piece of, a pair of like-polarity pole pieces.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A MAGNETIC RELAY HAVING IN COMBINATION TWO LATERALLY SPACED SETS OF POLE PIECES, EACH SET OF POLE PIECES DEFINING A GAP BETWEEN POLE FACES HAVING OPPOSITE POLARITY, MEANS FOR SUPPLYING EQUAL MAGNETIC FLUXES IN THE SAME DIRECTION IN EACH GAP, A MAGNETIC ARMATURE CENTRALLY PIVOTED BETWEEN SAID LATERALLY SPACED SETS OF POLE PIECES FOR ANGULAR DEFLECTION WITH RESPECT ENDS OF THE ARMATURE IN THE RESPECTIVE GAPS, MEANS FOR INDUCING AN UNBALANCING FLUX ALONG THE ARMATURE IN RESPONSE TO AN INPUT SIGNAL, AND A MAGNETIC INSERT POSITIONED BETWEEN THE LATERALLY SPACED POLE PIECES ON EACH SIDE OF THE ARMATURE, EACH SAID INSERT BEING SPACED FROM THE POLE PIECES AND THE ARMATURE TO DEFINE AIR GAPS THEREWITH. 